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Flame can infect PCs by offering itself as an update masquerading as official Microsoft software.

The heavy duty worm is snaking through systems mainly in the Middle East for the past two years or so on a reconnaissance mission. Now it has emerged that the malware uses a skeleton-key-like certificate found in Microsoft’s Terminal Services Licensing server to sign its malicious code and trick Windows machines into trusting and installing its executables.

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Microsoft customers that do no have their Windows Update software set to automatic configuration to install the latest patch immediately, which will thwart Flame’s man-in-the-middle attack.

While Microsoft goes over strategies to fight against Flame, other security experts continue to diagnose and analyze the mysterious malware and one researcher is showing how the virus can spread on local networks.

Cyber Security

“One of the methods (it can spread) is to hijack clients performing a Windows Update,” said virus protection provider Symantec. “Three Flamer apps are involved in delivering the rogue update: SNACK, MUNCH, and GADGET.”

SNACK tended to sniff out NetBIOS requests on LANs and would then imitate a Web Proxy Auto-Discovery Protocol (WPAD) server and feed a rogue configuration file (wpad.dat) to the local network, thereby effectively hijacking it and forcing traffic to redirect to the malware-infected machine, Symantec researchers said.

MUNCH, a web server within the Flame code, would then consume the redirected traffic, including matching URLs for Microsoft’s Windows Update software.

The final part of the puzzle was GADGET, a module Symantec said provided a binary signed by the dodgy Terminal Services certificate via the MUNCH web server that fooled the system into believing it was the genuine article from Microsoft.

“The binary is downloaded by the uninfected computer as if it is a legitimate Windows Update file and is executed. The binary is not Flamer itself, but a loader for Flamer. One sample of this binary refers to itself as TumblerEXE.exe,” Symantec said.

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